MacGameStore/Steam vs GOG.com (or, DRM vs price)

Was thinking about giving Witcher 2 Enhanced a go on my new iMac. It's about £14 on Steam, GOG.com and the Mac App Store, but about £7 on MacGameStore, which is a newish Steam-like service run by the website of the same name (which has been around a while I think).

It requires use of their app to install and I think run games you download from them. Ideologically I'm not a fan of that, even with Steam, so I don't really want another one. If I was going to get it at £14 I'd get it from GOG because there's no DRM there. But half the price from the new guys.

Then there's the question of which method gives the original devs the largest cut.* Anyone know?

* Yes, if I'm that worried about that I'd pay the higher price. Just wondering if it makes a difference. When a store cuts the price of a game, do they need the publishers permission?

@dominalien yeah, it's a lot higher than the minimum. Wouldn't have touched it otherwise but wanted a meaty game that wasn't an FPS or Civ (which I'm rubbish at) to play on it, this seems to fit the bill

Is Witcher 1 less good if I don't really have time for two massive RPGs?